A motor vehicle brake disc is oxidized by rainwater infiltrating from the outside and black rust sticks thereto. Such black rust leads to causes to impair the quietness and comfortability inside the motor vehicle. Accordingly, a motor vehicle brake disc is subjected to waterproof treatment to prevent oxidation.
Conventionally, for the purpose of preventing the black rust on a motor vehicle brake disc, there has been adopted a method in which a molded pulp product is directly fitted on a brake disc. However, such a molded pulp product is poor in water resistance, necessitates a number of steps for fitting and removing it, is high in cost and suffers other disadvantages; accordingly, there has recently been proposed the substitution of such a molded pulp product with a pressure-sensitive adhesive film (Japanese Patent Laid-Open No. 7-309510). Such a pressure-sensitive adhesive film is referred to as an antirust film, and is adhered to a tire wheel because the pressure-sensitive adhesive film has advantages such that it involves simple steps for adhesion and peeling and is capable of preventing the external flaw of the tire wheel. The antirust film is required to have three-dimensional curved surface followability because the tire wheel as an adherend has a three-dimensional curved shape. From such a viewpoint, flexible polyethylene film is used as a substrate film.
On the other hand, a motor vehicle chassis is aerodynamically designed, for the purpose of cooling the brake disc, in such a way that the air flow entering from the front of the motor vehicle is sucked toward tire wheels while the motor vehicle is running. Consequently, an air pressure is exerted from the inside on the antirust film. Thus, there is a problem such that the antirust film is peeled off when a motor vehicle is being transported on a carrier car or when a completed motor vehicle is being subjected to a running test.
Additionally, an aluminum wheel has an advantage that it is superior in workability to a stainless steel wheel, and hence sophistication of design has been advanced for aluminum wheels; aluminum wheels with thin spokes predominate from the viewpoints of mileage improvement by weight reduction, reduction of environmental burdens by decreasing the consumed amounts of materials, and improvement of cooling efficiency of brake discs. As a result, a reduced adhesion area is available for an antirust film to be adhered to an aluminum wheel, and hence there is a tendency that peeling problems are increasingly encountered.